The present invention relates to an apparatus for optically measuring a distance to a reflecting or scattering target object.
DE 197 27 988 A1 discloses a known apparatus for optical distance measurement to a target object consisting of a telescope, a distance measuring device, and an adjustment device for adjusting the laser beam divergence or the laser beam diameter. The distance measurement device comprises a beam source that emits a laser beam, a detector that receives a reception beam reflected and/or scattered at the target object, and a beam-shaping system with a transmission optical unit for shaping the laser beam, and a reception optical unit for shaping the reception beam. The laser beam divergence or the laser beam diameter may be modified by way of the exit angle of the laser beam at the beam source, a modification to the optical path length between the beam source and the transmission optics, or by additional transmission optics behind the beam source. The disadvantage is that all proposed measures for adjusting the laser beam divergence or the laser beam diameter within the distance measuring device reduce the stability of the distance measuring device.
An apparatus is known from DE 198 40 049 A1 for optically measuring the distance to a reflecting or scattering target object. The apparatus comprises a distance measuring device and an adjustment device for adjusting the laser beam to the target object. The distance measurement device comprises one or two beam sources, a detector, and a beam-shaping system with a transmission optical unit and a reception optical unit. The beam sources generate a first laser beam with a large beam divergence and a second laser beam with a low beam divergence, wherein the first laser beam is provided for the distance measurement of scattering target objects and the second laser beam is provided for the distance measurement of reflecting target objects.
The selection of a suitable laser beam may take place at the beam sources or at the detector. In one embodiment, the first and second laser beams are simultaneously emitted and strike the target object. In the beam path of the reception beam, optical filters are arranged in front of the detector that only let through the first or second laser beam. The optical filters are arranged in a manually operable or motor-driven filter wheel or filter slider, which introduce individual optical filters into the beam path of the reception beam. The disadvantage is that two laser beams with different beam divergences are required to adjust the distance measurement to the target object. To generate the different beam divergences, multiple beam paths and beam-shaping optics are required, which increase the space required.
The object of the present invention consists in developing an apparatus for the optical distance measurement for reflecting and scattering target objects, in which the number of optical components is reduced and in which the requirements placed on the production tolerances of the components is also reduced.
According to the invention, an adjustment device arranged outside the distance measurement device is provided with a second transmission optical unit, displaceable between a first and second position, for shaping the laser beam, wherein in the first position, the second transmission optical unit is arranged in the laser beam and in the second position, it is arranged outside the laser beam. The advantage of the second transmission optical unit is that the beam divergence, the beam diameter or the beam divergence and the beam diameter of the laser beam can be adjusted to the properties of the target object and/or the distance to the target object. By arranging the adjustment device outside the distance measurement device, the stability of the distance measurement device is not impaired. The emitted laser beam is collimated first by the first transmission optical unit and the collimated laser beam strikes the second transmission optical unit. Due to the fact that the collimated laser beam strikes the second transmission optical unit, the tolerance requirements imposed on the adjustment device are reduced compared to a design in which a divergent laser beam strikes the adjustment device.
Preferably, the distance measurement device has an optics carrier with a first mounting receptacle for attaching a first electro-optic component and a second mounting receptacle for attaching the first beam-shaping system. The optics carrier is constructed in a particularly preferred manner as monolithic and allows a compact structure of the distance measuring device. In a particularly preferred manner, the distance measurement device has a circuit board with a mounting receptacle for attaching a second electro-optical component and a connection device that connects the circuit board to the optics carrier.
In a preferred embodiment, the first transmission optical unit is constructed as a collimation optical unit and the second transmission optical unit is constructed as a scattering optical unit. The collimation optical unit of the distance measurement device generates a collimated laser beam that subsequently strikes the scattering optical unit of the adjustment device. The optical properties of the collimation optical unit are thereby adapted to scattering target objects and the scattering optical unit is provided for the distance measurement of reflecting target objects. The first position of the second transmission optical unit in the laser beam is provided for reflecting target objects and the second position of the second transmission optical unit outside the laser beam is provided for scattering target objects. The advantage of the collimation optical unit for measuring the distance of reflecting target objects consists of the requirements pertaining to production tolerances of the adjustment device and the precision during adjustment being reduced when a collimated laser beam, instead of a divergent laser beam, strikes the adjustment device.
In a particularly preferred manner, the adjustment device has multiple second transmission optical units for shaping the laser beam, wherein the second transmission optical units are constructed as scattering optical units with various expansion properties. In doing so, the expansion properties of the scattering optical units are adapted to various distance ranges of the reflecting target objects. To ensure that the laser beam is reflected on the target object and is detected as a reflected reception beam by the distance measurement device, a high degree of expansion of the laser beam is required at short distances to the target object. For large distances of the distance measurement device to the target object, a high degree of expansion of the laser beam would result in only a small portion of the laser beam being reflected at the target object and striking the distance measurement device as a reflected reception beam. If the intensity of the reception beam as measured by the detector is too low, the inaccuracy of the distance measuring increases. An adjustment device with various scattering optical units enables one to adjust the expansion of the laser beam to the distance range of the reflecting target objects.
An automatic selection of an appropriate scattering optical unit may occur in an iterative procedure. In a first step, a distance measurement takes place with a first scattering optical unit. The intensity of the measured distance value is compared against a specified value range. If the intensity falls below the lower value of the value range, the laser beam was excessively expanded; if the intensity exceeds the upper limit of the value range, the laser beam was not expanded sufficiently. If the measured intensity lies within the value range, the appropriate scattering optical unit is arranged in the laser beam. If the intensity lies outside the value range, a second scattering optical unit is arranged in the laser beam and another distance measurement is performed.
The distance value is again compared against the value range. It is advantageous to arrange the scattering optical units in an ascending manner (increasing beam expansion) or in a descending manner (decreasing beam expansion) in the laser beam. Fundamentally, it is also possible to freely select scattering optical units to determine the appropriate scattering optical unit in an iterative manner.
In a preferred design, the adjustment device comprises an optics wheel that is displaceable about a rotation axis. Multiple scattering optical units may be integrated into an optics wheel, which is constructed in a rotatable manner about a rotation axis, so that the expansion of the laser beam can be adjusted to the distance range of the reflecting target objects. An optics wheel has a small space requirement. The drive of the optics wheel may occur in a motor-driven manner by means of a motorized drive unit or be performed manually by the operator.
In an alternative design, the adjustment device has an optics slider that can be displaced along a translation axis. The drive of the optics slider may be executed in a motor-driven manner by means of a motorized drive unit or be performed manually by the operator.
In a preferred development, the adjustment device has a second reception optical unit, displaceable between a first and a second position, for shaping the reception beam, wherein in the first position, the second reception optical unit is arranged in the reception beam and in the second position, it is arranged outside the reception beam. The advantage of the second reception optical unit is that the properties of the adjustment device can be adjusted to the properties of the reflecting target object and/or the distance to the reflecting target object. With the help of the second reception optical unit, the reception beam reflected at the target object can be dampened to prevent one from overloading the detector.
In a particularly preferred manner, the first reception optical unit is constructed as a focusing optical unit and the second reception optical unit is constructed as a diffusing lens. The laser beam reflected at the target objects first strikes the diffusing lens. By means of the properties of the diffusing lens, the portion of the reflected laser beam that strikes the focusing optical unit can be adjusted.
In a particularly preferred manner, the adjustment device has multiple second reception optical units for shaping the reception beam, wherein the second reception optical units are constructed as diffusing lenses with various properties. The properties of the second reception optical units are thereby adapted to various distance ranges of the reflecting target objects. By means of the properties of the various diffusing lenses, the portion of the reflected reception beam striking the focusing optical unit can be adjusted.
In a preferred embodiment, the second transmission optical unit and the second reception optical unit are integrated into a common second beam-shaping optical unit. The second beam-shaping optical unit is thereby displaceable in a particularly preferred manner between a first and a second position, wherein in the first position, the second transmission optical unit is arranged in the laser beam and in the second position, it is arranged outside the laser beam, and in the first position, the second reception optical unit is arranged in the reception beam and in the second position, it is arranged outside the reception beam. Integrating the second transmission optical unit and the second reception optical unit into a common second beam-shaping optical unit simplifies the structure of the adjustment device and reduces the number of required components. The fewer the number of required components, the more compactly the distance measurement device and the adjustment device can be designed.
In a coaxial structure of the distance measurement device, the transmission and reception optical units are arranged coaxially to each other and in a para-axial structure of the distance measurement device, the transmission and reception optical units are arranged side by side.
Embodiments of the invention are described below using the drawings. It is not necessarily intended to portray the exemplary embodiments to scale; rather the drawings, where convenient for explanation purposes, are executed in a schematic and/or slightly distorted manner. In regard to supplements of the teachings readily evident from the drawings, one shall refer to the relevant prior art. One shall thereby take into account that diverse modifications and changes pertaining to the shape and detail of an embodiment may be undertaken, without deviating from the general idea of the invention. The features of the invention that are disclosed in the description, the drawings, as well as the claims may be essential individually per se as well as in any combination for the development of the invention. In addition, all combinations of at least two of the features disclosed in the description, the drawings, as well as the claims fall within the scope of the invention. The general idea of the invention is not restricted to the exact form or detail of the preferred embodiment depicted and described in the following, or to a subject matter that would be limited in comparison to the subject matter claimed in the claims. For given measurement ranges, values lying within the stated limits shall be disclosed as limit values and be usable and claimable as desired. For simplicity's sake, the same reference signs are used for identical or similar parts, or for parts with an identical or similar function.